The Limits of X-ray Diffraction Theory

What is it about?

All atoms vibrate and X-ray photons sample at the speed of light, therefore each atom diffracts a whole photon before it has barely moved. The crystal no longer appears as a perfect averaged array to a photon and results in intensity close to the Bragg angle remote from the Bragg condition. This effect is observed in experiments and simulations.

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Why is it important?

The Bragg condition is not necessary to form a diffraction pattern, which explains the data from XFELs and X-ray powder diffraction, and the transition between dynamical and kinematical theories. This changes the interpretation across a wide range of X-ray methods and creates new experimental opportunities.